Calcium metabolism in retinal rod outer segments during phototransduction is being studied with the aid of fluorochromic dyes introduced into retinas by new methods and studied by quantitative microscopic image systems. Calorimetric, X-ray microanalytic and photometric methods are being used to study ionic and biochemical events during phototransduction. New techniques for breaching the blood-brain barrier to introduce polar molecules into brain and retinal tissue are under study.